I. Types of Chemical Bonds Ionic Bonding Chemical bond made by attraction of oppositely charged atoms after the transfer of electrons between them 2 Na + Cl2 2 Na+Cl- (ionic compound) Metals lose electrons to become cations Na loses 1 e- [Ne]3s1 [Ne] Nonmetals gain electrons to become anions Cl gains 1 e- [Ne]3s23p5 [Ar] The +/- charge attraction in the NaCl molecule makes it 8.37 x 10-19 J more stable than 2Na and Cl2 apart. (Coulomb’s law) Ionic compounds stay bound together as solids, but dissolve in water to give separated cations and anions NaCl(s) + H2O(l) Na+(aq) + Cl-(aq) 3. Ionic Lewis Structure:

B. Formation of Binary Ionic Compounds 1. Lattice Energy = DE when separated gaseous ions pack to form a solid a. Exothermic process since attraction of ions is favorable b. Lattice Energy has a negative sign c. Calculate by summing steps: Example Li(s) + ½ F2 ----> LiF(s) 2. The Born-Haber Cycle: C. Lattices and Coulomb’s Law Larger charges (+2/-2) attract more CaO has > 4x the lattice E of NaF 1. Li(s) ----> Li(g) DE = +161kJ/mol 2. Li(g) ----> Li+(g) + e- DE = +520kJ/mol 3. ½ F2(g) ----> F(g) DE = +77kJ/mol 4. F(g) + e- ----> F-(g) DE = -328kJ/mol 5. Li+(g) + F-(g) ----> LiF(s) DE = -1047kJ/mol Li(s) + ½ F2(g) ----> LiF(s) DE = -617kJ/mol

Making Mg2+ and O2- ions requires More energy than making Na+ and F- Attractive forces of MgO >> NaF Lattice energy 4x greater, but overall energy difference is small

Predicting Formulas NaCl CaO D. Noble Gas Electron Configurations (NGEC) All elements react by gaining, losing, or sharing electrons to achieve the electron configuration of a noble gas (filled electron shells) Two nonmetals react: They share electrons to achieve NGEC. a. H (1s1) + H (1s1) H2 (1s2 = [He]) b. 2 Cl ([Ne]3s23p5) Cl2 ([Ar]) A nonmetal and a representative group metal react (ionic compound): The valence orbitals of the metal are emptied to achieve NGEC. The valence electron configuration of the nonmetal achieves NGEC. a. Na loses 1 e- [Ne]3s1 [Ne] Cl gainis 1 e- [Ne]3s23p5 [Ar] Ca lose 2 e- [Ar]4s2 [Ar] O gains 2 e- [He]2s22p4 [Ne] NaCl CaO

E. Use Periodic Table to predict charges and formulas Duet Rule: H and He always react to have 2 e- in outer (n =1) shell Octet Rule: All other main group elements react to have 8 e- in outer shell Transition metals and heavier metals: Harder to predict E. Use Periodic Table to predict charges and formulas MgxOy AlxSy CaxCly F. Ion sizes: More negative ions are larger, more positive are smaller Larger attraction for fewer electrons contracts cations: Ca > Ca+ > Ca2+ Less attraction for more electrons enlarge anions: O2- > O- > O O2> F > Na+ > Mg2+ > Al3+ Ions get larger down a group because larger shells are involved

Sizes of Ions Related to Positions of the Elements in the Periodic Table

G. Trends in Lattice Energies Increased charge leads to larger lattice energies Smaller ions lead to larger lattice energies H. Properties of Ionic Compounds High melting Points—strong attraction of full charges keeps ions together Conduct Electricity when dissolved in water—ions dissolve into water

I. Covalent Bonding Chemical bond formed by the energetically favorable sharing of electrons between 2 atoms Like charges repel each other with a similar strength that opposite charges attract one another +/+ proton/proton and -/- electron/electron interaction are unfavorable between any two bonded atoms The +/- attraction of an ionic bond overcomes this repulsion In covalent bonds, the atoms are neutral, so some other way of interaction must help overcome the +/+ and -/- repulsion Sharing the electrons between them can create 2 favorable +/- interaction The covalent bond will only form if the result is overall lower energy

In a covalent bond, the 2 atoms involved must come together until a minimum energy is found. Far away, there is no favorable interaction Closer together, the +/+ and -/- repulsions increase energy greatly If the atoms can share their electrons at lower energy, they form a covalent bond with a specific Bond Length Bond Energy = amount of energy required to pull them apart again H2 (covalent) is favorable, H+H- (ionic) is not

J. Polar Covalent Bonds Unequal sharing of the e- between two covalently bonded atoms This type of bond is somewhere between Ionic and Covalent A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment.

Electronegativity = attraction for shared electrons Electronegativity increases from left to right on periodic table Electronegativy decreases down a group The most electronegative atom in a bond has the electrons closest to it most of the time Atoms with the same electronegativities form purely covalent bonds Atoms with different electronegativities form polar covalent bonds

Bond Polarity and Dipole Moment Molecules with +/- ends have a dipole moment d tells us it is not a full charge Arrow points to negative end Complex molecule shapes: Dipole moments can cancel out to give a nonpolar molecule

K. Partial Ionic Character of Covalent Bonds Range of Bond Character Few bonds are purely Ionic or Covalent Most bonds have some character of both due to unequal electronegativity Calculating the Percent Ionic Character To compare molecules, we can calculate how Ionic they are Ionic Character increases as electronegativity difference increases No individual bonds are 100% Ionic (for the gas phase) Everything > 50% Ionic is considered Ionic in the solid phase Any melted compound that conducts electricity = ionic